Vulcanization of rubber and similar materials



Patented Aug. 9, 1932 UNITED STATES PATENT OFFICE SIDNEY M. CADWELL, OF GROSSE POINTE' PARK, MICHIGAN, ASSIGNCB TO THE NAUGAT'UCK CHEMICAL COMPANY, OF NAUGATUCK, CONNECTICUT, A CORPORA- TION OF CONNECTICUT VULCANIZATION F RUBBER AND SIMILAR MATERIALS No Drawing.

This invention relates to improvements in the treatment of rubber, and particularly in connection with the dry heat cure of rubber and similarvulcanizable material containing a an organic accelerator of vulcanization.

An object of this invention is to providean economical and improved method of dry heat curing rubber goods containing organic accelerators of vulcanization whereby the qualaa ity and appearance of said goods are enhanced. A further object is to provide in a method of dry heat curing rubber containing vulcanizing ingredients including certain accelerators of vulcanization, chemical means to for supplementing the vulcanization of said ingredients which means is also adapted to be diffused into the rubber during the vulcanizin treatment.

eretofore the curing of rubber goods in dry heat has required the use of organic accelerators in amounts from two to five times greater than those required for mold curing. A method of curing rubber stocks containing organic accelerators in dry heat has now been discovered wherein the amounts of organic accelerators employed may be markedly reduced below those normally required for dry heat cures, and being usually nogreater than those which would normally be used in a mold 80 cure. The method whereby the amounts of organic accelerators may be reduced as stated comprises vulcanizing rubber containing sulphur and such reduced amount of organic accelerator in an atmosphere containing ammonia, particularly in a closed type of vulcanizer at elevated temperatures and pressures.

Ammonia has been heretofore indicated as applicable in certain instances as a vulcanizing aid in the absence of organic accelerators. More recently ammonia has been indicated as a means of converting certain organic accelerators incorporated with the rubber into faster accelerators whereby the direct incor-- poration of the more owerful accelerators and the consequent risE of prevulcanization and burning on the mill may be avoided. In thelatter instance, the amounts of the particular organic accelerators to be used have been the full amounts normally required for Application filed November 2'7, 1931. Serial No. 577,703.

a dry heat cure, and the purpose of using the ammonia was to produce in the rubber after milling substantially the same or greater amounts of a particular faster accelerator-by a process of chemical conversion.

Accordingly the invention broadly comprises the vulcanization in an atmosphere containing gaseous ammonia of a rubber stock containing a vulcanizing agent and an organic accelerator said accelerator being employed in an amount substantially below that normally required for dry heat curing. Any recognized organic accelerator may be used, the following being given as typical:

(a) Aldehyde-awnin s.-Triethyltrimethylene triamine, heptaldehyde-aniline, ethylidine aniline, butyraldehyde butylamine,

butyraldehyde-aniline, and aldehyde derivatives of aldehydeamines such as the formaldehyde derivative of ethylidene-aniline and the acetaldehyde derivative of ethylideneaniline.

(b) Benzotkz'azyl sulphides.-Mercaptobenzothiazole, benzothiazyl disulphide, polynitroaryl benzothiazyl sulphides, such as 2-4 dinitrophenyl benzothiazyl sulphide, 2-6 dinitrol-chlorophenylbenzothiazylsulphide, 2-4-6 trinitrophenyl benzothiazyl sulphide.

(0) Esters and salts of ditkiocarbwmz'c ac idr-Polynitroaryl and arylmethylene esters of dithiocarbamic acid, for example, 2-4 dinitrophenyl dimethyl dithiocarbamate, and benzal bis (dimethyl dithiocarbamate), and metal salts of such acids, for example zinc salts thereof. v

(d) Organic s'uZphz'des.-T hi u r a m sulphides such as tetramethyl thiuram disulphide, tetramethyl thiuram monosulphide; carbalkoxythione sulphides such as oxynormal butyl thiocarbonic acid disulphide, and di-isopropyl xanthogen.

(e) Garbon bz'sul hide defioatzoes of aldehyde-ami1w.s.-Car on disulphide derivative ethylene polyamine condensation product,

propionaldehyde polyethylene polyamine condensation product, heptaldehyde-polyethylene polyamine condensation product, and the aldehyde derivatives of such condensation products. By polyalkylene polyamines are meant the higher boiling aliphatic bases prepared by reacting an alkylene dihalide with ammonia.

The following examples illustrate the effects of vulcanizing a stock containing no organic accelerator in the presence of ammonia, a d the combined efiect of an organic accelerato and ammonia on vulcanization, in one instance where normal amounts of accelerator are used and another instance where reduced amounts are used. The vulcanization is carried out on stocks of small thickness under commercial conditions using temperatures of vulcanization above 212 F.

The parts are by weight.

Ewample 1 typical shoe upper stock) A B C Pale crepe 39 39 39 Zinc oxide 4 4 4 Sulphur- 1 1 1 Lampblack 2.9 2.9 I 2 9 Gilders whiting 41. 4 41. 4 41. 4 Paraflin oil 3 3 3 'Iriethyltrimethyleue triamine p 1. 5

Green tcmile um Cute No 1 705 1870 1855 Cure No. 2 Uncured. 673 1671 Differences between N o. 1 and No. 2- 300 1197 184 I (Estimated) Cure No. 1 was carried out by placing the sheeted stocks into a closed type of vulcanizer connected to a tank of ammonia, closing the vulcanizer, and introducing ammonia gas until a pressure of 4 pounds per square inch was developed, after which the ammonia flow was cut oil. The temperature within the vulcanizer was raised gradually to 250 F. during 30 minutes and was so held at 250 F. for 60, minutes.

Cure N0. 2 was carried out under the same conditions of time and temperature as cure No. 1 but instead of using ammonia under pressure only air was introduced until a pressure of 4 lbs. per sq. in. was developed. Cure No. 2 represents an ordinary dry heat cure.

It is to be noted that the 1.5 parts of the; accelerator used in compound C above is representative of the normal amount of said accelerator required in ordinary dry heat cures. From the above data itwill be seen that stock B which contained one tenth (1/-10) of the normal amount of accelerator and was cured in dry heat in the presence of ammonia ac.- cording to this invention, was superior to stock C which contained a normal amount of accelerator and was subjected to an ordinary dry heat cure. It is also clear that the combined effect of the ammonia and of the reduced amount of organic accelerator operating jointly according to the present invention is far greater than the sum of the respective efiects when the ammonia and the organic accelerator are employed separately. Thus the amounts of organic accelerators which may be used in the process according to the present invention to produce well-cured'rubber stocks are entirely insuflicient to effect proper vulcanization in the usual process of dry heat curing. This is exemplified by the above and the succeeding examples.

Ewample 2 A stock made up of: Smoked sheet 100 Zinc oxide Lamp black 7 Gilders whiting 100 Spindle oil 10 Sulphur 2 Non-accelerating acetaldehyde condensation product (antioxidant) 3 and 1.25 parts of heptaldehyde-aniline con densation product diluted with spindle oil and sold under the trade name of Hepteen,

' are mixed on the rolls in the usual manner.

This stock is calendered to a thickness of .040 and laid on a steel surface, and placed in a pressure vulcanizer, which is then closed. Gaseous ammonia is introduced until a pressure of 6 pounds per square inch is developed. Air is then introduced until a total pressure of pounds per square inch is developed Heat is then applied so that the temperature within the vulcanizer rises to 240 .F. in the course of minutes. The temperature is then maintained at 240 F. for minutes.

The tensile obtained was 2106. The same procedure was repeated omitting the .ainmonia and the tensile obtained was .158 pounds per square inch. A similar stock containing 2.5 parts of the same accelerator was cured in air and the tensile displayed after cure was 443 pounds per square inch.

The stock cured in ammonia displays a hard, dry surface even when hot. It a es exceptionally well and shows a high res1st-. ance to breakdown duringflexing.

Example 3 A stock containing 100 parts of rubber, 10 parts zinc oxide, 3 parts sulphur, and .35

parts of polymerized triethyltrimethylene+ triamine is mixed on the rolls in theu'sual manner. A similar mix is madaco'ntaining- .7 part of the same accelerator. These stocks,

are calendered separately and placed in a jacketed heater; the heater is closed and ammonia is admitted to a pressurer of approximately 4 lbs. Air under pressure may or may not be admitted. In the present example no air other than that. originallypresent was admitted. Steam is admitted to the jacket of the heater at such a rate that the temperature of the interior of the heater rises to 240 F. in 30 minutes, and then from 240 to 270 in 60 minutes. The cures are then cgmplieted by heating for 20 minutes at 2 0 Similar stocks were made as above described, and cured as above described with the exception that 4 lbs. of air pressure was used and no ammonia gas was admitted to the heater. The data obtained from these experiments are as follows:

Pale crepe 100 100 Zinc Oxide 10 Sulphur 3 3 Triethyltrimethylene triamine .35 .70

(30' riseto 240 F. (60 rise 240 F. to 270 F. at 270 F.

Air 950 Ammonia and air 2560 Example J;

To show the results when various other types of accelerators are used in accordance with the invention a rubber master batch was compounded in the usual manner comprisin'g 100 parts of pale crepe rubber, 22 parts of lithopone, 8 parts of whiting, and 10 parts of zinc oxide. From this master batch were prepared a series of stocks'by the addition thereto of amounts of sulphur and accelerators as follows:

Accel- Sul- Aceel- Sul- Stock erator fur Stock orator fur 'letramethyl thiuramdisulflde A .5 2 E .25 1.5 Tetramethyl thiurammonosulphlde B 5 2 F 25 1. 5 2,4-dinitrophenyl dimethyl dithiocarbamate. C 1. 5 2 G 36 1. 5 Mercaptobenzothiazole. D s 1.5 2 H .50 1.5

The eight above-characterized stocks were cured under optimum conditions for each stock, as follows: Stocks A, B, C, and D containing normal amounts of accelerator required in the ordinary dry heat cure, were cured in a vulcanizer containing air at a pressure of lbs. per sq. inch according to the following schedule, which is representative of the usual practice: I

mins. rise from room temperature to 240 F., followed by mins. gradual rise;

from 240 to 250 F., the temperature then being held for 15 mins. at 250 F. in the case Tensile's (lbs. per sq. in.)

240 to 250 F., the temperature then being held for 30 mins. at 250 F.

Tensile tests following the cures gave the results indicated below (in lbs. per sq. in.)

Usual dry ea); cure (normal Dry heat; cure in presence of amount of accelerators) gg gg g gfg amounts Tensile at Tensile at break stock break A 2200 3630 B 2020 3500 C 1990 3130 D 2020 3420 The following table is further illustrative of the amounts of various accelerators which may be employed in carrying out the process of the present invention, and the amounts of the same accelerators which are required for the production of optimum cures accordin to the usual methods of dry heat curing referred to 100 parts by weight of rubber) Amount required Dry heat Ordinary cure with dry heat ammonia cure Tetramethyl thiuram disulphide; 0. l-0. l5 0. 35-0. 5 Tetramethyl thiuram monosulphide- 0. 1-0.15 0. 35-0. 5 Mcrcaptobenzothiazole 0. 3-0. 5 1.5 -2.0 2,4-dim'trophenyldimethyldithiocarbamate- 0.3-0.4 0.9 l.5 2 4-dinit-tophenyl benzothiazyl sulphide 0.4-0.5 3.0 4.0 inc djmethyl dithiocarbamate 0. l-0. l5 0. 25-0. 5 Polymerized triethyltrimethylene triamine. 0. 1-0. 5 1. 0 -2.0 Heptaldehyde-aniline (undiluted) about 0. 3 about 0. 5

In general, the amounts of various orgame accelerators required for successful practice of the present invention may range from about 10% to about of the amounts of the same accelerators required in the usual methods of dry heat curing.

This invention may be used to replace hot air cures of all types of vulcanized goods which are now given this cure. In carrying out the process of the invention ammoniapressures ranging from about 1 to about 10 lbs. per sq. in., with or without the use of additional air pressure, are preferable, although higher" ammonia pressures may be used, if desired. Instead of air, inert gases, such-as carbon dioxide or steam, may be used mixed with the ammonia. Articles of rub er footwear, raincoats, dipped goods,

tubi g, bathing caps, rubber blankets, water bottles, water toys, etc.

Rubber when vulcanized according to the processof the present invention allows of economies of operation and improvement in the'physical properties of the rubber goods definitely and favorably beyond that attendant the older method of producing vulcanized rubber goods by the dry heat air cure. There is a marked saving in the amount of organic accelerator beyond any normal expectation even though ammonia was found to operate to supplement its vulcanizing action to provide a satisfactory cure. Stocks prepared with the smaller amount. of accelerator have a much less tendency to burn on the mixing mill or to set up on standing, and when vulcanized under the conditions described show higher tensiles and as much as 100% better resistance to breakdown during mechanical flexing and definitely improved resistance to dete'rioration on standing, i. e. better ageing. Sun face oxidation during cure is substantially eliminated and the rubber shows a non-tacky fine hard shining surface even when hot, and does' not mar when handled in a warm condition, particularly when the gaseous pressure during the cure is greater than atmospheric. The efliciency of the accelerator, the time of cure, and the appearance of the finished article, are all more satisfactory when the conditions of this invention are followed than when those of ordinary dry heat air curing are carried out. This invention is particularly important in the field of footwear to produce articles that definitely outwear footwear vulcanized under the conditions of the old method of dry heat curing. Footwear upper stock produced accord'ng to the present invention has a finer appearance, withstands flexing better, is stronger, shows less surface deterioration and outwears footwear can Having thus described my invention, what I claim and desire to protect by Letters Patcut is: 1. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and an organic accelerator and vulcanizing the rubber in an atmosphere containing gaseous ammonia, said organic accelerator being employed in an amount insufficient to effect proper vulcanization in the absence of the ammonia. Y

2. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and an organic accelerator and vulcanizing the rubber in an atmosphere comprising air and ammonia, said organic accelerator being employed in an amount substantially less than that which would be required for an ordinary dry heat air cure.

3. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and an organic accelerator and vulcanizing the rubber in an atmosphere comprising air and ammonia, the partial pressure of the am monia being at least .about-l-pound per sq. inch, said organic accelerator being employed in an amount substantially less than that which would be required for an ordinary dry heat air cure.

4. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and an organic accelerator and vulcanizing the rubber in an atmosphere comprising air and ammonia, the partial pressure of the ammonia being at least about 1 pound per sq. inch, said organic accelerator being employed in an amount between about 10 and about percent by weight of the amount which would e required for an ordinary dry heat air cure.

5. A process of producing vulcanized rubber by dry heat whichcomprises incorporating into rubber a vulcanizing agent and an organic accelerator and vulcanizing the rubber in an atmosphere comprising air and ammonia, the partial pressure of the ammonia being at least about 1 pound per sq. inch, said organic accelerator being employed in an amount substantially equal to that which would be required for mold curing the same stock.

6. A processof producing vulcanized rubber by dry heat which comprises incorporat-- ing into rubber a vulcanizingagent and an organic accelerator, said organic accelerator being employed in an amount substantially less than that which would be requi ed for an ordinary dry heat cure, placing th stock in a vulcanizer, subjecting the stock to the action of a mixture of air and ammonia under superimposed pressure and raising the temperature in the vulcanizer, and completing the vulcanization of the stock at elevated temperatures in the presence of said mixture of air and ammonia. k

7. A process of producing vulcanized rub- IOU ber by dr'y heat which comprises incorporating into rubber a vulcanizing agent and an accelerating aldehyde-amine condensation product and vulcanizing the rubber in an atmosphere containing gaseous ammonia, said condensation product being employed in an amount insufficient to effect proper vulcanization in the absence of the ammonia.

8. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and an accelerating aldehyde-amine condensation product and vulcanizing the rubber in an atmosphere comprising air and ammonia the partial pressure of the ammonia being at least about 1 pound per sq. inch, said condensation product being employed in an amount between about 10 and about 60 percent by weight of the amount which would be required for an ordinary dry heat air cure.

9. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and an accelerating heptaldehyde-aniline condensation product and vulcanizing the rubber in an atmosphere containing gaseous ammonia, said condensation product being employed in an amount insufficient to effect proper vulcanization in the absence of the ammonia.

10. A process of producing vulcanized rubher by dry heat which comprises incorporating into rubber a vulcanizing agent and an accelerating heptaldehyde-aniline condensation product and vulcanizing the rubber in an atmos here comprising air and ammonia. said condensation product being employed in an amount substantially less than that which would be required for an ordinary dry heat air cure.

11. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and an accelerating mercaptothiazole and vulcanizing the rubber in an atmosphere containing gaseous ammonia, said mercaptothiazole being employed in an amount insufficient to effect proper vulcanization in the absence of the ammonia.

12. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and an accelerating mercaptothiazole and vulcanizing the rubber in an atmosphere comprising air and ammonia, the partial pressure of the ammonia being at least about 1 pound per sq. inch, said mercaptothiazole being employed in an amount between about 10 and about 60 percent by weight of the amount which would be required for an ordinary dry heat air cure.

13. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and mercaptobenzothiazole and vulcanizing the rubber in an atmosphere containing gaseous ammonia, said mercaptobenzothiazole being employed in an amount insuflicientto effect proper vulcanization in the absence of ammonia.

14. A process of producing vulcanized rubher by dry heat which comprises incorporating into rubber a vulcanizing agent and merca'ptobenzothiazole and vulcanizing the rubber in an atmosphere comprising air and ammonia, said mercaptothiazole being employed in an amount substantially less than that which would be required for an ordinary dry heat air cure.

15. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and an acceleratin thiuramsulphide and vulcanizing the rubber in an atmosphere containing gaseous ammonia,-said sulphide being employed in an amount insufficient to effect proper vulcanization in the absence of the ammonia I 16. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcaniz ng agent and an accelerating thiuramsulphide and vulcanizing the rubber in an atmosphere comprising air and ammonia, the partial pressure of the ammonia being at least about 1 pound per sq. inch, said sulphide being employed in an amount between about 10 and about 60 percent by weight of the amount which would be required for an ordinary dry heat air cure.

17. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and tetramethyl thiuram disulphide and vulcanizing the rubber in an atmosphere containing gaseous ammonia, said disulphide being employed in an amount insufficient to efi'ect proper vulcanization in the absence of the I ammonia.

18. A process of producing vulcanized rubber by dry heat which comprises incorporating into rubber a vulcanizing agent and tetramethyl thiuramdisulphide and vulcanizing the rubber in an atmosphere comprising air and ammonia, said disulphide being employed in an amount substantially less than that which would be required for ap ordinary dry heat air cure.

Signed at Detroit, County of Wayng, State of Michigan, this 23rd day of November,

SIDNEY M. OADWELL. 

